U.S. Pat. Nos. 3,941,615; 4,022,951 and 4,209,575 all disclose modular, multicell batteries of particularly unique configurations. In general, such multicell batteries comprise a plurality of frames, each of which is divided into a number of side-by-side active paste support areas. The frames are assembled and secured together in a stacked arrangement so that the perimeter partitions of the frames form the top, bottom and two opposite sides of the battery, and the divisions in the frames form cell partitions. Each frame is pasted with active material to form plates with adjacent plates in each frame being of opposite polarity and adjacent plates in each frame being of opposite polarity and adjacent plates in adjoining frames also being of opposite polarity. An electrolyte-porous separator material is provided between adjacent plates in adjoining frames.
U.S. Pat. No. 4,239,839 shows a similar type of configuration. However, in this configuration, a barrier frame is interposed and secured between, two frames in the assembly. This forms a chemical and electrical barrier between the active battery material in frames on opposite sides of the barrier member so that the assembly of frames can form two batteries having the desired voltage and/or capacity.
The modular, multicell battery described in the aforementioned patents represents a total departure from traditional, lead-acid battery constructions used for SLI automotive applications. Freed from the restrictions of a conventional premolded container, the capacity of such unique modular batteries can be increased merely by the addition of suitable grid frames with a separator frame placed in between.
The advantages are substantial. Such modular batteries may be produced in a highly automated manufacturing process and involve fewer components than are utilized in conventional lead-acid batteries.
Moreover, from the performance standpoint, such modular batteries with less weight can deliver equivalent performance to conventionally made lead-acid batteries. Indeed, such modular batteries can deliver up to 30% more current or power output per pound than a conventional lead-acid battery at 60.degree. F. and higher, due to the shorter current path and due to the lower solid electrical resistance component of the total battery electrical resistance. This accordingly means that, at such elevated temperatures, such modular batteries have lower electrical resistance than an equivalent size and capacity of a conventionally designed automotive battery. A further advantage is that there is no intercell connection failure mode in such modular batteries in comparison to conventionally designed automotive batteries in which intercell weld or connection failure is one of the principal failure modes in service.
The grids used in such modular batteries have been made using rolled strips or wrought alloys. Such strips are then slit or cut and expanded using reciprocating dies to form the mesh grids. This type of technology is well known. Typically, the formed grid mesh will have a thickness in the range of from about 20 to 40 mils or so. Likewise, commercially available modular batteries have utilized calcium-tin-lead alloys wherein the calcium content is relatively high, viz-in the range of from about 0.065 to about 0.08% by weight of the total alloy composition. The tin content in such alloys has been in the general range of about 0.5 to 0.8% by weight.
In recent years, due to various reasons, there has been a substantial increase in the under-the-hood temperature to which a battery is exposed in automobile service. This under-the-hood temperature is obviously higher in the warmer climates. One battery manufacturer has perceived that in past three years or so the temperature in such warmer climates to which an SLI battery is exposed in new automobiles has risen from about 125.degree. F. to 165.degree. F.
It is not particularly significant as to whether this particular level of temperature increase is what has occurred. What is significant is that, as a fact, the under-the-hood temperature conditions to which an SLI battery is exposed has risen significantly in new automobiles.
It has been discovered that, when modular batteries are placed in environments where relatively high temperatures are involved, premature battery failure due to positive grid corrosion can result. The possibility of such premature failure obviously lessens the utility of such modular batteries.
There has been a wide variety of calcium-tin-lead alloys which have been discussed in the patent and other literature for use in forming battery grids for conventional, lead-acid batteries. U.S. Pat. No. 2,860,969 to Walsh is thus directed to the inclusion of cerium as a grain refiner for lead-calcium, lead-tin-calcium, and lead-tin-silver-calcium alloys, which alloys can also contain small amounts of aluminum. The calcium contents disclosed range from about 0.03 to 0.1%.
U.S. Pat. No. 4,125,690 to Bagshaw et al. notes that, at calcium contents below 0.075%, the material is insufficiently hard within acceptable periods of time and that the corrosion of the alloy is greater as the tin content increases above 1%. Bagshaw et al found that greatly improved results were obtained with alloys having a selected combination of calcium, tin and aluminum. The calcium content in such alloys ranged from 0.075-0.13% by weight.
Further, the St. Joe Minerals Company publication by Rose and Young entitled "Lead-Calcium (-tin) Alloys: Properties and Prospects" discloses and describes a wide variety of calcium-tin-lead alloys together with the properties of both cast and wrought alloys. Table 2 sets forth the properties of five St. Joe alloys having calcium contents in the range of from 0.03 to 0.06% and 0.3 to 1.5% tin.
The foregoing prior work are only illustrative examples of the work that has been carried out. Substantial work on calcium-tin-lead alloys has been undertaken in conjunction with use in maintenance-free batteries.
Despite this wide variety of interest and discussion of a wide variety of alloys, there is little direction that would permit the selection of an alloy composition that would have enhanced positive grid corrosion resistance, particularly when exposed to relatively high temperature conditions. This is particularly true for the unique modular, multicell batteries previously described.
It is accordingly an object of the present invention to provide a modular, multicell battery capable of a satisfactory service life when exposed to relatively high temperature environments.
Another and more specific object provides a frame having a grid made from an alloy that imparts to the resulting battery enhanced positive grid corrosion resistance.
Other objects and advantages will be apparent as the following description proceeds, taken in conjunction with the accompanying drawings.